make `raco test' more like `racket'

Instad of `(dynamic-require .. #f)', use `(dynamic-require .. 0)', which
has the effect of making compile-time code "available" (see docs) in
case the loaded module uses `eval' on syntax objects that refer to
non-kernel syntax.
add v5.3.3 notes
restore changes that don't go into 5.3.3
2d
Increase timeout for TR random testing.
preserve lexical context, src, etc for sequence syntax expansion

The previous version of the code replaced the implicit #%app with
the kernel #%app (ie, #%plain-app), causing sequence functions
that take keyword arguments to fail.
Post-release version for the v5.3.3 release
dont use raco test for encode.rkt (as it expects command-line
arguments and doesn't have a test submodule)
change raco test's announcements to say "raco test"
move dir-chars.rkt to unstable/2d to unbreak dependencies
tweak raco test output, yet again
unbreak plai random mutator tests
Add a test for PR 13490

The bug itself was already fixed by Eric Dobson
Make static single flonum checks correct.

Closes PR13499.
Add extra tests and warning about -PosIntNotFixnum.
adjust test cases for recent changes to the lexers
New Racket version 5.3.3.1.
Supporting headers and stateless in web-server/test
Fix :print-type. Closes PR13503.
Make overlap more precise.